The operator of a diesel engine, in a vehicle or other application, frequently has three operational engine controls. There is an electrical switch for actuating a starter motor and a mechanical linkage to a throttle to govern engine speed, corresponding to the basic controls for a gasoline engine; the diesel engine also has a run/stop control. This latter control actuates a run/stop member on the governor for the fuel pump of the engine and must be actuated (rotated) from a STOP position to a RUN position in order to condition the fuel pump of the diesel engine for operation.
Two different kinds of actuator linkage have been employed for the run/stop member of the fuel pump governor of a diesel engine. The simplest and most direct actuator is a cable connection or other mechanical linkage from the run/stop member to a plunger or lever accessible to the vehicle operator. However, many manufacturers and users of equipment powered by diesel engines consider a mechanical linkage of this kind undesirable. This has led to adoption of solenoid actuators, in which the plunger of a solenoid is connected to the run/stop member on the fuel pump governor so that energization of the solenoid drives the run/stop member to its RUN position permitting operation of the engine. When the solenoid is de-energized, its internal spring, or another spring mechanism, returns the plunger to an initial position and rotates the run/stop member of the governor to its STOP position, shutting off operation of the fuel pump. In some installations, the electrical switch for energization and de-energization of the solenoid is combined with the electrical switch for the starter motor so that the overall control is essentially a duplicate of that for a conventional gasoline engine with electrical ignition. In this way, the diesel engine control is more familiar to a greater variety of operators.
Solenoid actuators for the run/stop governor control in a diesel engine encounter several technical difficulties, particularly in the crowded conditions prevalent in many diesel engine installations. The fuel pump and its governor, in a vehicular diesel engine or other engine installation, are often quite inaccessible due to many other equipment items mounted in the engine compartment. Thus, mounting of a solenoid actuator for the run/stop control member of the governor, in the engine compartment, often presents a serious problem with respect to determination of a mounting position that will allow a connection between the solenoid plunger and the run/stop member. Furthermore, due to manufacturing variations, and particularly variations in engine mounting, individual adjustment of the length of the connecting linkage between the solenoid plunger and the run/stop member is almost always essential and quite critical. In this respect, it may be noted that if the solenoid does not provide for an adequate stroke upon energization, the maximum rated fuel flow for the engine cannot be realized and the available power is undesirably reduced.